The drush version command is an example of a command that returns
a simple string result. A label, "Drush Version", is also defined
for the data, and this is printed when drush version is executed
in its default format of key-value.  When output in string format,
then only the data itself is shown.
<p>
<i>$ drush version --pipe</i>
<pre>
6.0-dev
</pre>
<p>
Code:
<pre>
return DRUSH_VERSION;
</pre>
